We will learn pump basics in this article. So, what is pump? Let us try to understand. When we required to lift fluid from a lower elevation to a higher elevation, external equipment is required. This equipment is the pump.

Around 20% of the world’s electrical power is consumed by pumps in many ways.

What is Pump & Basics?

Let’s concentrate on the basics of the pump. Pumps are used almost all kinds of,

• domestic,
• industries,
• various plants,
• medical,
• commercials,
• agricultural,
• wastewater service,
• chemical & food processing,
• oil and gas sectors,

to lift or transfer fluids from one place to another.  

Pump Definition

The pump has a driving component that is a motor (sometimes may be an engine), and a power source is connected to the motor.

• Once the pump is switched ON, electricity is supplied to the motor, and
• the pump does a mechanical action and changed the electrical energy into hydraulic energy, and
• lifts or transfers fluids from a lower elevation region to a higher elevation region.

Hence, A pump is defined as the mechanical equipment which lifts or transfers fluids from a lower elevation region to a higher elevation region. by converting electrical energy into hydraulic energy.

• Pumps are of various types.
• These are operating based on various design principles.
• Working philosophy are different for different pumps.
• It needs a driver to operate.
• Driver may be motor or engine or gas or turbine etc. driven.

Function of Pump

The main function of pumps are as follows,

• Pump lifts liquids from lower elevation to higher elevation.
• It helps to circulation liquids from one point to another point.
• It increases the pressure or the head of pump to meet the required discharge pressure requirements.
• If a system loss the pressure, pumps are used to increase the pressure of the system to make it stable.
• Pumps are used to transfer required liquid flow rate.

Check a NICE ANIMATED video to understand the pump basics!

Pump Basics Terms

To understand the pump or it’s working principle, there are few pump basics terms are required to know. These are.

• Volumetric flow rate
• Shut-off head
• Suction Head 
• Static suction head (hs)
• Suction lift
• Static discharge head (hd)
• Friction head
• Total Head 
• Vapor pressure
• Net Positive Suction Head
• Specific speed

Volumetric Flow Rate

Volume flow rate means the capacity of the liquid per unit time which is transfer through the pumps.

• It is the rate of water flow.
• Pump capacity is expressed in volumetric flow rate and head.
• It is measure in m³/s or ft³/s.

The volume of flow, ‘V’ and time is ‘t’, then the volume flow rate,

q = V/t

If the mass flow rate is ‘m, and density is ‘ρ’, and the volume flow rate,

Then, we can write,

m = ρ x q,

or, q = m/ρ

Hence, it can be defined as the ratio of mass flow rate to the density.

In S.I. units, the volumetric flow rate is measure in m³/s and F.P.S unit, it is measured in ft³/min.

Shut-off head

The shut-off head is one of the most important parameters in the pump. It is defined as the head with respect to zero volumetric flow rate.

Static head

Static head means the height difference between the elevation of source of liquid and elevation of the discharge liquid.

• Suction static head is totally depending on the elevation.
• It doesn’t depend on the flow rate.
• It depends on the specific gravity of the liquid, at a given pressure.

Static suction head

Static suction head is a part of static head.

• It is used when liquid source is above the pump center line.
• It describes the height from the liquid source to the pump center.
• Normally it is denoted by ‘hs’.
• This value is considered as +ve.
• Doesn’t depend on the liquid flow rate.
• Depends on the specific gravity, at a given pressure.

Suction Lift

• This term is used when pump is placed above the liquid surface, elevation wise.
• This is the vertical distance between the liquid surface and the pump center line, when pump is placed above.
• This height is limited to 10m, due to the limitation of atmosphere.
• This value is considered as, -ve, as it is always opposite direction to static suction head.

Static discharge head  

Static discharge head is also a part of static head.

• It is used to specify the distance between the elevation of the liquid in the destination and the pump center line.
• Normally it is denoted by ‘hd’.
• Doesn’t depend on the liquid flow rate.
• Depends on the specific gravity, at a given pressure.

Friction head

Pump has piping system and all pipe will have many fittings, bends, straight length based on the system design. Hence, these all provide the resistance to the flow which is required to overcome so flow will be continuous in the system.

This head is known as friction head & it is the loss that needs to overcome.

The friction head depends of the following,

• Size of the pipe
• Pipe condition
• Age of pipe
• Type of pipe
• Nos of fitting
• Nos. of bends
• Pipe length
• Total system configuration
• Liquid flow rate
• Type of liquid

Total Head

Total head in a system is defined as the total pressure difference between inlet and outlet of the pump.

• In case of source is above the pump, difference between the discharge head and the suction head plus the friction head.
• In case of source is below, it is the sum of discharge head, suction lift, and friction loss.
• TDH = Static Height + Static Lift + Friction Loss

Vapor Pressure

AT a given temperature, vapor pressure is the pressure which is exerted by the gas in equilibrium with either a solid or liquid in a closed container.

• It is the pressure, in which molecules enter the vapor state at a specified temperature. If you boil a liquid, you can observe it.
• It is simply an indication of the evaporation rate of the liquid.
• If the temperature increases, vapor pressure will also increase.

Various units are used for vapor pressure:

• Pascals (Pa),
• bar (bar),
• tor (mm Hg),
• atmospheres (atm),

Net Positive Suction Head

The Net Positive Suction Head – NPSH – is defined as the difference between the Suction Head, and the Liquids Vapor Head

and can be expressed as

NPSH = hs – hv,

Where,

Hs – Suction head

Hv – Liquid vapor head             

There are two terms which is very important,

• NPSHr
• NPSHa

NPSHr 

NPSHr means NPSH required for the pump selection. It is one of the main function for the selection of pumps so that pump will not have any cavitation problem during operation.

• It is the lowest value of NPSH in which pump will run without any cavitation.
• It is normally provided by manufacturer.
• Best wat way to determine it by actual testing.
• NPSH-R is the value at which the discharge pressure is reduced by 3% because of the onset of cavitation.

NPSHa 

NPSHa means NPSH available. It is calculated from the suction side of the pump.

It is basically a function of the system based on which a pump operates.

NPSHa when pump is below the source,

NPSHa = Pa + hs – pv – pf

Where,

• Pa – Absolute pressure head on the liquid surface
• Hs – static head above pumps center line
• pv – absolute liquid vapor pressure head at pumping temperature
• pf – the suction friction head losses.

NPSHa when pump is above the source,

NPSHa = Pa – hsl – pv- pf

NPSH-A is always more than NPSH-R for any operating conditions to avoid cavitation of pumps.

Specific speed

Specific speed or pump specific speed is defined as the parameter to specify the size or shape of pump impeller. It is dimensionless parameter.

Specific speed means, the followings,    

• It helps to select appropriate impeller size.
• It depends on shaft speed.
• It also depends on the flow rate and differential head at BEP.
• It is essential when comparison between two pumps are required.
• It doesn’t depend on pump size.

The friction head depends of the following,

• Shaft speed
• Flow rate
• Differential head etc.

Specific Speed is written mathematically, as follows,

Ns = n q^1/2 / h^3/4        

Where

Ns = specific speed

n = pump shaft rotational speed (rpm)

q = flow rate (m³/h, l/s, l/min, m³/min, gpm (US & British) at Best Efficiency Point (BEP)

h = head rise (m, ft)

Specific speed is used to:

• Hydraulic design
• Pump performance
• Impeller size, as well as trimming

After pump basics, let get into the types of pumps.

Types of Pumps

Pumps are classified into two main groups, and it is further classified into many groups.

Types of Pumps

• Positive Displacement Pump
• Dynamic Pump

Positive-Displacement Pumps

As the name suggests, positive displacement pump means associated with the displacement of fluids. This pump transfers a fluid by trapping a fixed amount of fluid and displaced it into the discharge section.

It takes some amount of fluid from one end, that is the suction side and positively displaced in the discharge side.

• It is generally used for pumping oil wells and viscous liquids applications.
• In this pump, volume at each cycle of operation is constant.
• A positive-displacement pump does not have shutoff head.
• Safety of relief valve is necessary at the he discharge side for safety purpose.
• This pump cannot operate at discharge valve closed condition. In case it operates, discharge pipe or the pump will be damaged.

Positive-displacement types

A positive-displacement pumps are classified into three types,

• Rotary-type 
• Reciprocating-type 
• Linear-type 

Rotary Pumps

Rotary pump transfers fluids by using a rotating mechanism. It creates low pressure or vacuum and take up the fluids from the source. After taking up, due to the rotation, fluid is transferred.

• These pumps have rotating parts and stationary parts and the clearance between these parts is very small.
• Small clearance helps to minimize the leakage to the suction side from the discharge side.
• These are normally used for high viscosity liquids.
• Designed considering lower speeds.

Advantages 

• Very efficient for viscous fluids.
• No separate priming is required.
• It can handle more fluid, than the reciprocating pump at same weight.

Disadvantages 

• Due to low clearances between the stationary and rotating parts, speed is low.
• High speed may cause erosion and reduce the efficiency.

The classification of these types of pumps depends on the types of rotating elements and they include:

• Gear pumps
• Lobar pumps
• Screw pumps
• Labyrinth pumps
• Vane pumps
• Radial-plunger pumps
• Vibratory pumps.

Reciprocating Pumps

Reciprocating pumps have piston and cylinder arrangement and due to the reciprocating motion of the piston in the cylinder, the pump works.

Cylinder has suction and discharge side with valves. Piston moves and creates low pressure to draw the fluid. After suction, piston pushes back and create the pressure on the fluid and fluid discharge with high pressure.

• It is widely used in high pressure and low flow applications.
• Works based on reciprocating action.

Advantages 

• It can produce high head.
• No priming required.
• It provides high suction lift.
• Air can be used.  

Disadvantages 

• High maintenance.
• Low flow.
• Difficult for high viscous fluids.

The classification of these types of pumps depends on the types of rotating elements and they include:

• Plunger pumps 
• Diaphragm pumps 
• Piston pumps 
• Radial piston pumps 

Linear Pumps

In this type of pump, as the name suggest, the displacement of the fluid happens linearly.  

• In a linear pump, no calibration is required.
• Due to the linear motion of the piston, it creates noise.
• It is installed at a faraway distance from people.  

These pumps are different kinds, like,

• Rope pumps
• Chain pumps

Positive Displacement Pump Advantages

• Widely used for dosing and injection pumps
• High-pressure application
• Suitable for high viscous fluids
• Very good suction capacity, even with gas content
• Suitable for high viscosity
• This pump has the provision to adjust the stroke to adjust the flow rate. 
• It is suitable for low-flow applications as well.
• It is suitable for low drive speeds. 

Disadvantages of positive displacement pumps

• Many parts associated with wearing.
• A pressure relief system is a must from the safety point of view.
• It can produce noise.
• Suitability is reduced for high-speed operation.

Dynamic Pumps

Centrifugal force is the main driving force in dynamic pumps. Due to this force, pump develops velocity in the liquid. This velocity is converted into pressure.

• It has impeller which creates low pressure in order to draw fluid.
• Widely used for low viscosity fluids.
• High flow rate, low pressure applications.
• Low maintenance

Dynamic Pumps are classified into two types:

1. Horizontal Centrifugal Pumps
2. Vertical Turbine Pumps

Centrifugal Pumps

Centrifugal pumps are used to transfer liquid by converting mechanical energy into hydraulic energy.

This pump creates centrifugal force by the rotation of impeller.

• It transfers transfer liquid from one place to another place.
• The main force is centrifugal force
• Kinetic energy changed into a pressure head.
• Pumps are driven by motor or engine, as applicable.

Horizontal Centrifugal Pumps are classified into three types:

1. Axial flow pump
2. Radial flow pump
3. Mixed flow pump

Axial Flow Pump

In this kind of pumps, casing splits axially.

Radial Flow Pump

In the case of Radial split pump, casing splits radially.

Mixed Flow Pump

Combines radial and axial flow, producing a conical flow pattern around the impeller shaft.

Vertical Turbine Pumps

As the name suggests, these kinds of pumps are vertical. Vertical turbines are widely used for pumping in the following industries,

• Irrigation system,
• Power plants,
• Steel plants, etc.

Parts of a Pump

There are basics parts of the pump, based on the types of pumps. We have already learned parts of the pump for reciprocating pumps, like:

• Suction Pipe
• Suction Valve
• Delivery Pipe
• Delivery Valve
• Cylinder
• Piston and Piston Rod
• Crank and Connecting Rod
• Strainer
• Air Vessel

In the same way, parts of the pump for Centrifugal Pumps, are as follows:

• Casing
• Impeller
• Suction pipe with a foot valve
• Strainer and
• Delivery pipe etc.

Parts of pumps are illustrated for centrifugal pumps and reciprocating pumps, as these are the widely used pumps in various industries.

How Does a Pump Work?

There are so many types of pumps and the working principle of each pump is different. However, the basic principle is the same and here, we are going to explain how does a pump work in general.

Let’s get in the step-by-step explanation!

Step#1 Start of Driver

The pump is connected to a motor or engine or any other driver and the driver is required to starts to operate.

Step#2 Intake of Fluid

We have already learned that pumps transfer fluid from one place to another. Hence, it is necessary to get the fluid into the pump. In case of reciprocating pumps, a negative pressure is created in the cylinder due to the movement of the piston.

However, priming is required for the centrifugal pump, as the impeller cannot create much pressure difference in the pump.

Step#3 Limitation of Negative Pressure

Pressure should not be below the vapor pressure, else, bubbles will be formed and cavitation can occur which will damage the pump.

Step#4 Increase in Pressure Energy

In a centrifugal pump, volute and diffuser help to increase the pressure of the fluid. Centrifugal force is created due to the rotation of the impeller and this force is acted on the fluid too.

Water is transferred through the volute (gradually increased cross-section) and velocity is reduced which further converted into pressure.

In case of a reciprocating pump, the piston is connected to the crank through the connecting rod, and the crank is connected to a driver. After sucking the fluid, the piston moves opposite, and pressure is generated on the fluid.

Hence, we have got the basics of the pump working philosophy.

Pump Power Calculation Basics

Theoretical Pumping Power

Theoritical Pump power calculation, P

Here, P = = ρ x g x q x h,

Where,

P = Power, in Watt

ρ = Density of fluid, kg/m³

g = Gravitational acceleration, m/s²

q = Flow rate, m³/s

h = Head, m

Actual Pumping Power

Actual Pump power calculation, P’

Here, P’ = Theoritical pumping power / pump efficiency

P’ = ρ x g x q x h / η

[Where, η = efficiency of pump]

Advantages of Pumps

These are many advantages of Pump, as follows:

• Pumps are very useful equipment to transfer fluids.
• It is available from a very small capacity to a very large capacity.
• It is widely used as circulating equipment in many systems like chilled water circuits, cooling tower circuits, and many more.
• Noise is less comparative with other rotating devices.
• Pumps can be used (reciprocating pump) for gaseous applications as well.
• No leakage, fewer losses.
• A wide range of constructions, a wide variety of materials is used for pumps.

Disadvantages of Pump:

These may be some disadvantages as well of Pump:

• Operation of pumps is smooth, however, it may be encountered cavitation. It hurts the pump.
• The pump can have corrosion problems.
• Many times, handling fluids may have problems. For example, reciprocating pumps are not suitable for viscous fluids.
• Centrifugal pumps cannot work without priming.
• There is a limitation of piston or impeller speed.

Applications of Pump:

The application of pump is wide, few of them are listed below:

• Water storage & transfer.
• Domestic application.
• Sewage & slurries application.
• Fire fighting & protection system
• Manufacturing, chemical, oil & gas, pharmaceutical, food, aviation, HVAC, etc. industries.
• Aquarium, water fountain, and pond filtering, etc.
• Even in the automobile sector, pumps are used.
• In thermal power plants, or nuclear power plants, or hydroelectric power plants, pumps are one of the vital equipment.

Conclusion

Hence, we have got an idea about the pump basics along with an understanding of what is pump, its parts, working principle, etc. Any questions, please write to us.